Process of roasting zinc-blende.



UNITED STATES-frills if} CHARLES A.

No Drawing.

To all whom it may concern.

lie it known that 1. CHARLES A. H. on Sarrtns, a citizen of the UnitedStates, and resident of the borough of Manhattan, city, county, andState of New York, have invented certain new and useful Improvements inProcesses of Roasting Zinc-Blende; and I do hereby declare the followingto be a full, clear, and exact description of the invention. such aswill enable others skilled in the art to which it appertains to make anduse the same.

In the. roasting of zinc blende as a preliniinary operation to therecovery of zinc in the form of spelter in the usual retort furnace,there remain in the roasted ore constituents which have a prcju .licialeffect upon the retort process. These constituents, not reduied in thecustomary roasting operation, have. in part. the ctl'ect of producing aslag of such relatively high basicity as to corrode the walls and bottomof the retort: in part, also. they have as a result the production of alarge quantity of gas which in making its exit from the retort undulyspeeds the Zinc vapor-s as they pass through the condenser. so that someof the zinc va por is carried out of the condenser and is thus lost inso l ar as the production of spelter is concerned: and. finally. sullltof the ingredients left in the roasted charge are of such a character asto give up sulfur contained in them to the zinc vapors. resulting in theformation of zinc sultid. which is likewise lost in so far as theproduction of spelter is concerned. So also. in the practical operationof the speltcr retort when applied to the production of spelter fromroasted blende. a considerable portion of the time required for thecomplete treatment of the charge is absorbed in the preliminaryreduction in the retort of these prejlulicial ingredients. In theendeavor to overcome these diszulvantages, .l have ascertained that theycan be largely minimized by adding to the charge. in the tinal stage ofthe roasting operation. a quantity of carbon (for instance. anthracitecoal) and by regulating the combustion of the carbon tor the purpose notonly of obtaining a reducing ell'ect upon the deleterious ingredients inquestion. but also of realizing a temperature high enough to effect th*additional advantage of dissociation of such deleterious ingredients byheat. without. however. volatilizingany of theZinc or other metals. Thehigh temperature due I themselves, as above indicated.

to the combustion of the carbon is like assisted by the exothermiccharacter of the resulting reactions, to the correspomling benefit ofthe reducing and dissociation effects desired.

In the practical application of my invention, when the roastingoperation is carried on, for instance, in a roaster of the well knownMatthiessen and Hegeler type, or the like, I add the carbon upon thelast or next to the last hearth of the series and in such manner as tomaintain as nearly equal a distribution in carbon as is possible,throughout the charge. I then regulate the air blast to such a degree asto initiate the reduction or dissociation, as the case may be, if thedeleterious ingredients, the temperature thus realized beingcorrespondingly increased by the exothermic character of the reactionsThe effect of this procedure is manifold. In the first place, the zincsulfate present in the charge will be dissociated, its sulfur ingredientpassing ott and leaving zinc oxid. Secondly, the sulfates of lead,barium and calcium present are reduced to snltids of lead, barium andcalcium, so that the subsequent spelter retort process is relieved ofthe burden of reducing them, and so that there is a corresponding lesserproduction of gases in the spelter retort. The. sulfate of magnesiumpresent is reduced to magnesium oxid, which, in sharp contrast to thetrouble usually attendant in the retort process upon the presence ofmagnesium therein is harmless to the retort and is even beneficial inthat it. tends to stiffen the slag therein. l urthermore, the Fed).present is reduced in part to metallic iron in part to Fed) and in partto bet), in which form they are of less deleterious elfect upon theretorts. lt is also evident. of course. that the aggregate amount ofsulfur present in the charge is likewise diminished. The net result ofthe procedure described to relieve the retort process of a considerableproportion of the burden usually imposed upon it. Such reduction anddissociation as take place in the roasting operation. as practised inaccordance with my inventii'in. is found to result in so relieving thespelter retort operation that the zinc vapor begins to distil from theretorts from one to two hours earlier than in the usual practice. and.without lengthening the period of operation in the rctorts. and. in fat. even slmrteniug that operation, a longer period nevertheless obtainedfor the zinc distillation p01 80, inasmuch as the distillation beginsearlier. So also, the loss of sulfur which, in the usual operation isattendant upon the production of an excessive amount of gas, which tendsto push the zinc vapors through the condenser, is correspondinglydiminished.

In the ordinary practice, the magnesium sulfate present in the charge isreduced in the retorts to magnesium sulfid, and the latter in beingfurther changed to magnesium oxid gives up its sulfur to the zinc in theform of zinc sulfid, thus increasing the zinc loss. In the practice ofmy invention, this source of zinc loss is entirely removed and themagnesium oxid is even made available to the advantage of the operationin stifiening the slag and counteracting the formation of fusible slags,as specified. Finally, the highly basic Fe O usually present is, byreduction outside of the retorts, in accordance with my invention, madeharmless by conversion, as described, into metallic iron and into osidsof lower oasicity.

In actual practice, my process has resulted in raising the percentage ofZinc recovered from roasted zine blende of inferior quality, from an 80per cent. recovery under the customary practice, to 88 per cent.recovery, and has diminished the retort loss from 1.6 retorts per ton ofore smelted to 1 retort. I may say, further, that'many of the advantages due to the reduction and dissociation of the deleteriousingredients of roasted Zine blende as hereinbefore described, arelikewise realizable not only in the subsequent treatment of the roastedproduct in the usual retort process, but also in the electric zinefurnace process, wherein the presence of such ingredients is likewise tobe avoided. I have found that the reduction and dissociation of thecompounds, in accordance with my invention, can be effected, at the hightemperatures required, without causing any noticeable loss of zinc orother metals; that is to say, the reduction and dissoeiation in thefinal stage of the roasting operation requiring a temperature which,al-' though in excess of the temperatures employed in ordinary roastingare nevertheless below the temperatures which would result in anymaterial loss of zinc or other metals.

In carrying out the invention as hereinbefore described, I add carbon,preferably in the form of fine anthracite coal, at the latter part ofthe roasting operation equal to about eight per cent. in weight of thecharge of the Zinc ore and so regulating the air supply, by anyappropriate means for controlling the air inlets, that the temperaturedue to the combustion of the added carbon shall not exceed 1000 degreesC., and, preferably, attains a maximum of 880 degrees (3., the latterprecaution being necessary to avoid volatilizing any of the zinc orother metals in the preliminary roasting operation.

\Vhen the process is applied as a preliminary to the electric zincfurnace process. preferably from fifteen to twenty per cent. of carbonin the form of fine coal is added to the roasting charge toward the endof the roasting operation which, in addition to the advantageshereiubefore indicated, has thev desirable and necessary effect of alsopreheating the charge before it is delivered to the electric furnace.

What I claim is CHARLES A. H. DE SAULLES.

VVitnesses:

H. A. PROSSER, M. A. GATELY.

